1. Field of the Invention
The present invention provides an improved air filter, or filter, for internal combustion engines and particularly adapted for use with motorcycles, the filter having different airflow resistance at different portions thereof.
2. Description of the Prior Art
Air filters designed for use with internal combustion engines have been available for many years. The air filter is typically installed in an air-filter case mounted beneath the seat and is connected to carburetor through the intake pipe.
Conventional air filters for off-road motorcycles are typically shaped as a conical frustum having a cavity opening at its inner section. The conventional air filter is typically made in a wet sponge format, i.e. foam sponge is immersed in viscous oil and then used with the air filter. In order to prevent reduced airflow due to dust deposits, the wet sponge filters utilize a double-layered structure wherein a coarse sponge is placed on the air filter outer layer and a covering a fine sponge placed as the inner layer. The sponges typically are the same thickness.
It is known that air filters are essential to protect the engine from dirt and sand in order to ensure its durability; engines having low ventilation resistance are considered desirable because airflow injected into the engine creates resistance. Current air filters seek the ability to block dirt and sand and injected air resistance, airflowing evenly from many directions at the same time. In this regard, and referring to FIGS. 7-9, conventional air filter 50 utilizes different sponges 51 and 52 for its outer and inner layers, each sponge being made of the same material and of the same thickness for the entire surface area. This allows the same amount of air to flow into the air filter 50 from all surface areas. That in turn causes the air 51 flowing from the side-surface section to collide with the air 52 flowing from the bottom surface section on the inside of the air filter 50 causing air turbulence. As a result the air intake to the engine decreases, decreasing engine efficiency.
U.S. Pat. No. 4,039,308 to Schiff (Schiff) discloses a device formed of rigid foam material which functions both to filter and straighten air introduced thereto prior to being directed to the vehicle air intake. Specifically, the device comprises an integral air filter and air straightening means made of the same porous material. The air straightening means performs two functions, i.e. that of cleaning air introduced thereto in a manner similar to that accomplished by an air filter while also reducing the turbulence of the cleaned air before being introduced to an air intake device, such as a carburetor.
Although the air fitters disclosed in the conventional arts, such as illustrated in Schiff, provide an increased flow of cleaned air at the air intake of the internal combustion engine, the airflow comprises two components having two different velocity vectors; the resultant mixed airflow reducing the total amount of useful airflow to the air intake, thus reducing engine efficiency. What is desired is to provide a simple, yet cost efficient, light weight air filter that creates increased airflow into the engine, thus increasing engine efficiency.